Biological tissues produce a wide variety of electrophysiological signals to convey information throughout the nervous system and to trigger muscle contractions. Sensing and monitoring these voltages or “biopotentials” is an important function for a wide variety of medical devices and scientific instruments. Examples of commonly observed biopotentials include the electroencephalogram (EEG) measured from the scalp; the electromyogram (EMG) measured in or near muscles; the electrocardiogram (ECG) measured on or near the heart; the electrocorticogram (ECoG) measured from the surface of the brain; local field potentials (LFPs) measured in the brain; and single-unit recordings of individual neurons in the brain or nerve fibers.